Tumors and lesions are types of pathological anatomies characterized by abnormal growth of tissue resulting from the uncontrolled, progressive multiplication of cells, while serving no physiological function.
Pathological anatomies can be treated with an invasive procedure, such as surgery, but can be harmful and full of risks for the patient. A non-invasive method to treat a pathological anatomy (e.g., tumor, legion, vascular malformation, nerve disorder, etc.) is external beam radiation therapy. In one type of external beam radiation therapy, an external radiation source is used to direct a sequence of x-ray beams at a tumor site from multiple angles, with the patient positioned so the tumor is at the center of rotation (isocenter) of the beam. As the angle of the radiation source changes, every beam passes through the tumor site, but passes through a different area of healthy tissue on its way to the tumor. As a result, the cumulative radiation dose at the tumor is high and the average radiation dose to healthy tissue is low.
The term “radiotherapy” refers to a radiation treatment procedure in which radiation is applied to a target region for therapeutic, rather than necrotic, purposes. The amount of radiation utilized in radiotherapy treatment sessions is typically about an order of magnitude smaller, as compared to the amount used in a radiosurgery session. Radiotherapy is typically characterized by a low dose per treatment (e.g., 100-200 centiGray (cGy)), short treatment times (e.g., 10 to 30 minutes per treatment) and conventional or hyperfractionation (e.g., 30 to 45 days of treatment). For convenience, the term “radiation treatment” is used herein to mean radiosurgery and/or radiotherapy unless otherwise noted by the magnitude of the radiation.
In order to deliver a requisite dose to a targeted region, whilst minimizing exposure to healthy tissue and avoiding sensitive critical structures, a suitable treatment planning system is required. Treatment plans specify quantities such as the directions and intensities of the applied radiation beams, and the durations of the beam exposure. It is desirable that treatment plans be designed in such a way that a specified dose (required for the clinical purpose at hand) be delivered to a tumor, while avoiding an excessive dose to the surrounding healthy tissue and, in particular, to any important nearby organs. Developing an appropriate treatment planning system is especially challenging for tumors that are larger, have irregular shapes, or are close to a sensitive or critical structure.
A treatment plan may typically be generated from input parameters such as beam positions, beam orientations, beam shapes, beam intensities, and radiation dose distributions (that are deemed necessary by the radiologist in order to achieve a particular clinical goal). Sophisticated treatment plans may be developed using advanced modeling techniques, and state-of-the-art optimization algorithms.
Two kinds of treatment planning procedures are known: forward planning and inverse planning. In early days, treatment planning systems tended to focus on forward planning techniques. In forward treatment planning, a medical physicist determines the radiation dose of a chosen beam and then calculates how much radiation will be absorbed by the tumor, critical structures (i.e., vital organs) and other healthy tissue. There is no independent control of the dose levels to the tumor and other structures for a given number of beams, because the radiation absorption in a volume of tissue is determined by the properties of the tissue and the distance of each point in the volume to the origin of the beam and the beam axis. More specifically, the medical physicist may “guess” or assign, based on his experience, values to various treatment parameters such as beam positions and beam intensities. The treatment planning system then calculates the resulting dose distribution. After reviewing the resulting dose distribution, the medical physicist may adjust the values of the treatment parameters. The system re-calculates a new resulting dose distribution. This process may be repeated, until the medical physicist is satisfied by the resulting dose distribution, as compared to his desired distribution. Forward planning tends to rely on the user's ability to iterate through various selections of beam directions and dose weights, and to properly evaluate the resulting dose distributions. The more experienced the user, the more likely a satisfactory dose distribution is produced.
In inverse planning, in contrast to forward planning, the medical physicist specifies the minimum dose to the tumor and the maximum dose to other healthy tissues independently, and the treatment planning module then selects the direction, distance, and total number and intensity of the beams in order to achieve the specified dose conditions. Given a desired dose distribution specified and input by the user (e.g., the minimum and maximum doses), the inverse planning module selects and optimizes dose weights and/or beam directions, i.e. select an optimum set of beams that results in such a distribution.
Inverse planning may have the advantage of being able to produce better plans, when used by less sophisticated users. However, conventional treatment planning systems do not allow a user the flexibility to use both forward planning and inverse planning techniques within a same plan, or to switch back and forth between forward planning and inverse planning. Also, conventional treatment planning systems do not allow a user to incorporate direct modification of the topological map for the isodose distribution. These conventional inverse planning systems may require user definition of anatomical regions to affect the dose distribution. These drawn regions may usually cover a limited percentage of the patient anatomy, and may not fully reflect the clinical goals of the treatment plan. Further, existing treatment planning systems may be based solely on either an isocentric beam geometry or a non-isocentric boundary-targeting beam geometry.